1. Field of the Invention
The present invention relates to a composite microsize cable construction having as one element an optical fiber for transferring laser energy and as another element, a pair of electrical leads for transferring temperature sensing signals.
2, Related Applications
This application relates to application Ser. No. 003,209, filed Jan. 14, 1987, entitled "Laser Angioplasty Probe", now U.S. Pat. No. 4,760,845 and application Ser. No. 180,188 filed Apr. 11, 1988 entitled "Laser Heated Probe and Control System".
3. Description of the Related Art
An extensive review of related prior art is given in the referred to copending related applications. Such review is incorporated here by referene and is repeated here only as necessary for background to the present invention.
A relatively recent medical procedure in laser angioplasty is that of indirect laser irradiation. In this procedure, laser energy is transmitted by a microsize e.g 300 microns, optical fiber at a power level of a few watts, e.g. one to sixteen or more watts, to a site to be treated such as an arterial or venous channel blocked by plaque At the site, the laser energy is converted to thermal energy by use of a thermally conductive device which is brought in contact with the plaque, thrombic complex or the like to melt or evaporate the channel blocking material.
The Federal Republic of Germany Pat. No. 2,826,383 published Dec. 20, 1979 is cited along with other references in U.S. Pat. No. 4,646,737 and 4,662,368. The earlier German patent as well as the two later U.S. patents disclose a heat generating element in the form of a metal probe mounted on an optical fiber through which light is transmitted to generate heat energy in the heat generating element. The German patent mentions but does not describe or illustrate use of a thermocouple and does not disclose means for controlling the temperature of the heat generating element.
U.S. Pat. No. 4,476,512 illustrates a system which is apparently directed to the direct laser irradiation technique since the patent makes no disclosure of using light energy to heat a probe or the like. This patent nevertheless illustrates a heat sensitive element, i.e. a thermistor, positioned on the surface of the output end of an optical fiber as a means of sensing abnormal changes in the surface temperature of the fiber at its output end. The lead from the temperature sensor is not described as to its composition and is illustrated as being a separate element from the cable which carries the optical fiber.
The substantially different characteristics of optical fibers and electrical leads and substantially different requirements for laser energy and temperature sensing signal transmissions within the body have apparently deterred prior attempts to provide a composite microsize cable in which both an optical microsize fiber of appropriate character and microsize temperature sensor leads of appropriate character have been formed into a common cable construction of microsize and suited to use in an angioplasty procedure. Thus, the primary object of the invention becomes that of providing such a cable. Other objects will become apparent as the description proceeds.